This invention relates to an assembly and method for retaining circuit board assembly components. More specifically, this invention relates to an assembly and method for retaining a processor power pod to a printed circuit board.
The process of manufacturing computer systems includes assembling the necessary electronic components. Often times the electronic components are fragile, and may become damaged during assembly. For example, when components such as processor power pods are installed on a board using threaded fasteners such as screws, tolerance stack up between mated parts may result in power pod retention screws being seated too deeply. Screws that protrude too deeply may lead to board damage in the form of shorting between voltage and ground planes of the board.
Various attempts have been made in the past in order to overcome the problem of board damage caused by fasteners. FIG. 1 is a cross-sectional view, illustrating a method currently utilized in the industry for fastening processor power pods to boards. A retainer 2 is secured to a printed circuit board 4. The circuit board 4 is a multi-laminate board, including a layer of copper with an epoxy laminate on its top surface. This configuration permits higher density routing of signal traces through voltage and ground planes. The retainer 2 contains threaded inserts 6 that rest flush against the circuit board 4, specifically the epoxy laminate layer. The threaded inserts 6 include internal threads 8 and a top surface 10. Processor power pods 12 are housed in die cast aluminum shells, and each shell includes mounting flanges 14 containing through-holes 16.
The currently utilized method for fastening processor power pods to boards includes placing a power pod 12 on a board 4 while ensuring the through-holes 16 of the power pod flanges 14 line up with their corresponding retainer threaded inserts 6. A retention screw 18 is then inserted through each power pod flange through hole 16, as illustrated in FIG. 1, engaging the threaded insert 6 of the retainer 2 to retain the power pod 12 to the board 4.
Although the size and length of the screw 18 is selected for a particular application in an attempt to avoid contact with the surface of the circuit board, it has been recognized that the distal end of the screw 18 may nevertheless contact the board in certain circumstances. For example, the flanges 14 are of different thicknesses depending upon the particular power pod 12 or location on a particular power pod 12, and this variation, combined with tolerance stack up between the associated mated parts (screw 18, retainer 2, and threaded insert 6), contributes to the retention screws 18 either travelling too deeply through the retainer threaded inserts 6, or not deeply enough to adequately engage the inserts 6. For example, if the threaded portion of the screw 18 is too long (i.e., beyond the expected length tolerance) and/or the power pod flange 14 is too thin (i.e., below the expected thickness tolerance), then the screw 18 may contact the board. Conversely, if the threaded portion of the screw 18 is too short and/or the power pod flange 14 is too thick, then insufficient engagement of the threads may result. Screws 18 that protrude too deeply may lead to board damage in the form of shorting between voltage and ground planes of the board. Screws 18 that do not travel deeply enough will not adequately retain the power pod 12 to the board 4.
Accordingly, there is a need for an assembly and method that can overcome tolerance variations while safely and effectively retaining components such as processor power pods to printed circuit boards.
This invention provides a fastener assembly configured to engage a component to a circuit board assembly having a circuit board and a retainer positioned adjacent the circuit board. The fastener assembly comprises an elongated member extending between proximal and distal ends. The member includes a proximal portion having threads, and a distal portion having threads configured to engage the retainer of the circuit board assembly. A shoulder is spaced from the distal end of the member, and is configured to contact a surface of the retainer and to limit the travel of the distal end of the member toward the circuit board. The distance between the distal end and the shoulder of the member is equal to or less than the distance between the surface of the retainer and the circuit board, thereby reducing or eliminating interference between the distal end of the member and the circuit board. The fastener assembly also comprises a fastener adapted to engage the threads of the proximal portion of the member. The fastener is configured to engage the component to the circuit board assembly.
This invention also provides a method for engaging a component to a circuit board assembly having a circuit board and a retainer positioned adjacent the circuit board. The method includes the step of engaging a distal portion of a stud to the retainer of the circuit board assembly. The method also includes the step of contacting a shoulder of the distal portion of the stud to a surface of the retainer, thereby limiting the travel of the distal end of the stud toward the circuit board, and thereby reducing or eliminating interference between the distal end of the stud and the circuit board. The proximal portion of the stud is extended through an aperture in the component, thereby positioning the component adjacent the retainer. A fastener is then engaged to a proximal portion of the stud, thereby engaging the component with respect to the circuit board assembly.